Digital images for assessing soil cover of crop plants

Summary

The main drawback by using crop soil cover in weed harrowing research is that it is assessed by visual scores, which are biased and context dependent. This problem may be solved by using digital image analysis. In this paper a new image capture standard and digital image analysis procedure was used to illustrate three key issues in relation to weed harrowing; selectivity, resistance and recovery. All issues require reliable assessments of crop soil cover. Crop soil cover was deduced from assessments of leaf cover, which is defined as the proportion of pixels in digital images determined to be green.
Objective assessments of leaf cover and crop soil cover showed that the selectivity of weed harrowing in winter wheat and spring barley was unaffected by timing within a two weeks interval. Crop recovery, defined as the ability of the crop to recover from soil cover was determined in winter wheat and highly influenced by timing of weed harrowing. Increasing intensities of harrowing in growth stage (BBCH) 22 in winter wheat increased crop yields whereas crop yields declined by increasing intensities in growth stage 23 due to differences in the crop recovery capacity. Resistance defined as the capacity of the crop to resist soil cover was tested in barley, field pea and mixtures of barley and field pea. No differences were found between the crops. Future aims in mechanical weed control research are discussed in the context of the availability of unbiased crop soil cover data.